The present invention relates to an electric apparatus such as a notebook PC (notebook personal computer) and in particular to an electric apparatus to which a charge-discharge battery can be connected.
Secondary batteries, which can be repeatedly reused by recharging after they are discharged, are widely used in electric apparatuses such as notebook PCs, for example. Nickel-cadmium batteries (nicad batteries), lithium ion batteries, and the like are typically used as the secondary batteries. Also, lithium polymer batteries, which are safe and suitable for slim designs, will come into widespread use.
An electric apparatus such as a notebook PC uses as its secondary battery a main battery which it included in it as standard equipment. In addition to this main battery, a “sub-battery”, which is an optional expansion battery, is used in some electric apparatuses. Conventionally, these electric apparatuses using a sub-battery besides the main battery discharges the sub-battery first, then, after remaining charge in the sub-battery becomes 0% (nearly 0%) of full charge, switches to the main battery and discharges the main battery until its remaining charge becomes 0% (nearly 0%).
Typically, square lithium ion cells are used in a sub-battery, for example. The sub-battery using lithium ion cells has high internal resistance and contains a fuse and therefore a large discharge current may cause high self-heating. In recent years, the maximum power consumption in a notebook PC has increased. When a program that places system hardware such as its CPU in full operation is executed, a discharge may cause an excessive rise in temperature. In such a case, a protect function may be activated in order to protect the apparatus against the excessive temperature rise in the battery cells and as a result, the apparatus may shut down.
FIG. 6 shows data on temperatures during discharging according to a background art. The horizontal axis indicates time and the vertical axis indicates temperatures. Shown in FIG. 6 are data on temperatures in a sub-battery protection FET, sub-battery cells, main battery protection FET, and main-battery cells, and ambient temperature.
Assumption here is that the CPU is operating in normal mode and a current of 5,500 mA flows from the battery cells. The maximum power consumption of the CPU is high and the temperature of the sub-battery protection FET and sub-battery cells rises with time. It can be seen that at the first point of time in FIG. 6 the CPU enters low-speed mode because of an excessively large current, resulting in reduction in performance. As a result, the temperature of the sub-battery protection FET drops temporarily but then continues to rise. On the other hand, the temperature rise slope of the sub-battery cells becomes slightly gentle after the first point of time but continues to rise. At the second point of time at which the temperature exceeds 60Â° C. (at the point where it rises to 63Â° C., for example), a protect circuit within the battery may be activated to shut off power supply from the sub-battery to the system. Such unexpected shutoff of power supply from the sub-battery to the system is undesirable.
The present invention has been made in order to solve the problem and a purpose of the present invention is to prevent shutoff of electric power supply from a battery to a system.
Another purpose of the present invention is to prevent shutdown of a plurality of separate battery units and use them to the fullest.